Effects of pre- and post-reinforcer delays on choice in pigeons

Abstract

The present study examined effects of pre-and post-reinforcer delays on pigeons' choice using concurrent-chains schedules. Subjects were exposed to concurrent-chains schedules in which a single variable-interval 30-s schedule was arranged for the initial link, followed by different fixed-time schedules for pre-and post-reinforcer delays as the terminal links. The pre-and post-reinforcer delays were fixed at 2 s for one alternative and they were manipulated across conditions (2 s, 8 s, 20 s, or 40 s) for the other alternative. Based on the sensitivities estimated from the overall reinforcement density model, it is suggested that pigeons have higher sensitivity to the pre-reinforcer delay relative to the post-reinforcer delay. These results are consistent with those reported in a previous study using rats. Comparisons of choice proportion data from different post-reinforcer delays reveal that pigeons have sensitivity to post-reinforcer delay, although it is not high.

Computerized intertemporal choice task in chimpanzees (Pan troglodytes) with/without postreward delay.

“…This is in line with observations that several animal species exhibit a level of self-control that is best explained by maximization of the short-term reward rate, which is insensitive to PRD and ITI (i.e., reward amount divided by reward delay; starlings [ Sturnus vulgaris ]: Bateson & Kacelnik, 1996; blue jays [ Cyanocitta cristata ]: Stephens & Anderson, 2001; tamarins [ Saguinus oedipus ]: Stevens et al, 2005). Indeed, some studies have shown that animals are sensitive to PRD to some extent, but the sensitivity to PRD is much smaller than the sensitivity to the reward amount and delay (e.g., pigeons [ Columba livia ]: Hata & Saeki, 2018; Logue et al, 1985; rats [ Rattus norvegicus ]: Yamaguchi et al, 2015). If the difference in PRD between two options is ignored, the long-term reward rate obtained by choosing either option would be misestimated, which may be consistent with the hyperbolically discounted value derived from ITC behavior in many species (Hwang et al, 2009; Kirby & Maraković, 1995; Mazur & Biondi, 2009).…”